The majority of smokers in the U.S. would like to quit. Despite declines in cigarette use during the past several decades, smoking remains common (21%) among U.S. adults and is the leading preventable cause of death. Tobacco control efforts have greatly reduced smoking prevalence (from 43% in 1964). However, extensive evidence shows that the decline in smoking prevalence has stagnated for the past 10 years. The reasons for this stagnation are unknown. While tobacco control efforts have been very successful, ultimately, these strategies may not reach all smokers. Therefore, the proposed study will examine whether the prevalence of specific factors that impede successful quitting have become more common among smokers over the past two decades. We will also examine potential pathways through which these factors may lead to persistent smoking. The results of this study will lead to a better understanding of the barriers to cessation among remaining smokers, informing the debate over how to lower the prevalence of smoking in the US.